Poisonous Plants (Monotonic Stack)

System Design: Multi-Carrier Package Delivery System Design a system to deliver customer packages that supports multiple delivery partners/carriers such as UPS, USPS, FedEx, etc. Your design should cover: Core entities (Shipment/Package, Customer, Address, Carrier, Tracking Event, Label, Rate, Manifest, etc.) APIs to create shipment, get rates, buy label, schedule pickup, track shipment, and handle delivery exceptions Integration approach for multiple carriers (adapters/plugins, normalization of statuses, retries, idempotency) Data model and storage choices Asynchronous processing (webhooks, polling, event bus) Reliability and observability (DLQ, monitoring, tracing) Security and compliance (PII, authn/authz) Scalability considerations